Semiconductor device

ABSTRACT

A semiconductor device includes a semiconductor element having first and second main surfaces spaced apart in a thickness direction. The semiconductor element includes a metal underlying layer on the first main surface, a bonding pad on the metal underlying layer with a wire bonded to the pad, and an insulative protection layer formed on the first main surface and surrounding the bonding pad. The bonding pad includes first and second conductive layers. The first conductive layer covers the metal underlying layer and is made of a metal having a lower ionization tendency than the metal underlying layer. The second conductive layer covers the first conductive layer and is made of a metal having a lower ionization tendency than the first conductive layer. The first and second conductive layers have respective peripheries held in close contact with the protection layer and covering a part of the protection layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device.

2. Description of the Related Art

Various types of semiconductor devices have been proposed that perform aspecific function on the basis of inputs and outputs of a current froman external device, for example as disclosed in JP-A-No. 2002-76051. Theconventional semiconductor device of this document includes asemiconductor element, a bonding pad, a protection layer, a wire, and alead frame. The bonding pad is formed on the semiconductor element. Theprotection layer is also formed on the semiconductor element. Theprotection layer is located adjacent to the bonding pad, so as to coverthe periphery of the bonding pad. The wire is bonded to the bonding padand the lead frame.

The bonding pad is formed by stacking a metal, for example Al(aluminum). To bond a wire to the bonding pad, a wire, which is made ofe.g. Cu (copper) and provided through a bonding tool such as acapillary, is molten and pressed against the bonding pad by the tipportion of the capillary, and ultrasonic vibration is applied. In thisprocess, since Al is a relatively soft material, fragments of thebonding pad may disperse or the pad may crack due to the pressure andvibration applied during the wire bonding.

Further, in a conventional semiconductor device of JP-A-No. 2002-76051(FIGS. 2 and 3), the periphery of the metal layer formed by stacking aplurality of metal films is covered with a protection layer, and theexposed portion of the upper face of the metal layer is serves as abonding pad. With this configuration, however, the metal layer is formedover a larger region than the exposed portion as the bonding pad, whichis disadvantageous to making the semiconductor device smaller in size.In addition, the protection layer covering the periphery of the metallayer may detach from the metal layer. When the underlying metal layeris exposed owing to the detachment of the protection layer, theuncovered portion of the metal layer may be corroded, and the durabilityof the semiconductor device may be degraded.

SUMMARY OF THE INVENTION

The present invention has been proposed in view of the foregoingsituation. It is therefore an object of the invention to provides asemiconductor device that can be manufactured in a smaller size and withimproved durability.

According to an aspect of the present invention, there is provided asemiconductor device is provided with: a semiconductor element includinga first main surface and a second main surface that are spaced apartfrom each other in a thickness direction; and a wire. The semiconductorelement includes: a metal underlying layer formed on the first mainsurface; a bonding pad formed on the metal underlying layer and to whichthe wire is bonded; and an insulative protection layer formed on thefirst main surface and surrounding the bonding pad as viewed in thethickness direction. The bonding pad includes: a first conductive layercovering the metal underlying layer and made of a metal having a lowerionization tendency than the metal underlying layer; and a secondconductive layer covering the first conductive layer and made of a metalhaving a lower ionization tendency than the first conductive layer. Thefirst conductive layer and the second conductive layer have peripheries,respectively, that are in close contact with the protection layer andcover a part of the protection layer.

Other features and advantages of the present invention will become moreapparent from the detailed description give below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a semiconductor device according toa first embodiment of the present invention;

FIG. 2 is a plan view of the semiconductor device shown in FIG. 1, witha sealing resin indicated by imaginary lines;

FIG. 3 is an enlarged fragmentary cross-sectional view of a part of FIG.1;

FIG. 4 is an enlarged fragmentary cross-sectional view of a part of FIG.3;

FIG. 5 is a fragmentary cross-sectional view showing a manufacturingprocess in a manufacturing method of the semiconductor device shown inFIG. 1;

FIG. 6 is a fragmentary cross-sectional view showing a process thatfollows the process of FIG. 5;

FIG. 7 is a fragmentary cross-sectional view showing a process thatfollows the process of FIG. 6;

FIG. 8 is a fragmentary cross-sectional view showing a process thatfollows the process of FIG. 7;

FIG. 9 is a fragmentary cross-sectional view showing a process thatfollows the process of FIG. 8;

FIG. 10 is a fragmentary cross-sectional view showing a process thatfollows the process of FIG. 9;

FIG. 11 is a fragmentary cross-sectional view showing a process thatfollows the process of FIG. 10;

FIG. 12 is a fragmentary cross-sectional view showing a process thatfollows the process of FIG. 11;

FIG. 13 is a fragmentary cross-sectional view showing a process thatfollows the process of FIG. 12;

FIG. 14 is an enlarged fragmentary cross-sectional view of a variationof the semiconductor device according to the first embodiment of thepresent invention;

FIG. 15 is an enlarged fragmentary cross-sectional view of a part ofFIG. 14;

FIG. 16 is an enlarged fragmentary cross-sectional view of anothervariation of the semiconductor device according to the first embodimentof the present invention;

FIG. 17 is an enlarged fragmentary cross-sectional view of a part ofFIG. 16;

FIG. 18 is an enlarged fragmentary cross-sectional view of asemiconductor device according to a second embodiment of the presentinvention;

FIG. 19 is an enlarged fragmentary cross-sectional view of a part ofFIG. 18;

FIG. 20 is a fragmentary cross-sectional view showing a manufacturingprocess in a manufacturing method of the semiconductor device shown inFIG. 18;

FIG. 21 is a fragmentary cross-sectional view showing a process thatfollows the process of FIG. 20;

FIG. 22 is a fragmentary cross-sectional view showing a process thatfollows the process of FIG. 21;

FIG. 23 is a fragmentary cross-sectional view showing a process thatfollows the process of FIG. 22;

FIG. 24 is an enlarged fragmentary cross-sectional view of asemiconductor device according to a third embodiment of the presentinvention;

FIG. 25 is an enlarged fragmentary cross-sectional view of a part ofFIG. 24;

FIG. 26 is a fragmentary cross-sectional view showing a manufacturingprocess in a manufacturing method of the semiconductor device shown inFIG. 24;

FIG. 27 is a fragmentary cross-sectional view showing a process thatfollows the process of FIG. 26;

FIG. 28 is a fragmentary cross-sectional view showing a process thatfollows the process of FIG. 27;

FIG. 29 is a fragmentary cross-sectional view showing a process thatfollows the process of FIG. 28;

FIG. 30 is an enlarged fragmentary cross-sectional view of a variationof the semiconductor device according to the third embodiment of thepresent invention; and

FIG. 31 is an enlarged fragmentary cross-sectional view of a part ofFIG. 30.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described belowwith reference to the accompanying drawings.

FIG. 1 to FIG. 4 illustrate a semiconductor device according to a firstembodiment of the present invention. The semiconductor device A1 of thisembodiment includes a semiconductor element 1, wires 2, a main electrode31, sub electrodes 32, and a sealing resin 5. FIG. 2 is a plan view ofthe semiconductor device shown in FIG. 1, the sealing resin beingindicated by imaginary lines. FIG. 3 is an enlarged fragmentarycross-sectional view of a part of FIG. 1. FIG. 4 is an enlargedfragmentary cross-sectional view of a part of FIG. 3. In FIG. 4, thewires 2 and the sealing resin 5 are omitted.

The semiconductor element 1 is configured to perform a desired function,and may be exemplified, without specific limitation, by a transistor, adiode, a capacitor, and so forth. As shown in FIG. 1, the semiconductorelement 1 includes a first main surface 10 a and a second main surface10 b. The first main surface 10 a and the second main surface 10 b areoriented in opposite directions to each other, in a thickness directionof the semiconductor element 1 (Z-Z direction in FIG. 1). On the firstmain surface 10 a, a non-illustrated functional circuit that realize thefunction of the semiconductor element is formed. The second main surface10 b in contact with the main electrode 31. The semiconductor element 1is manufactured, for example, from a wafer made of Si.

As shown in FIG. 2 and FIG. 3, the semiconductor element 1 includes ametal underlying layer 11, an insulation layer 12, bonding pads 13, anda protection layer 14. The metal underlying layer 11, formed on thefirst main surface 10 a, is made of a metal such as Al. The metalunderlying layer 11 has a thickness of, for example, 0.5 μm to 5 μm.

The insulation layer 12, formed on the metal underlying layer 11, ismade of an insulative material such as SiO₂. The insulation layer 12 is,for example, formed so as to surround a predetermined region of arectangular shape. The insulation layer 12 has a thickness of, forexample, 0.1 μm to 0.5 μm.

As shown in FIG. 2, the protection layer 14 surrounds the bonding pads13 in a view in the thickness direction of the semiconductor element 1.As shown in FIG. 3, the protection layer 14 is formed on the first mainsurface 10 a. The protection layer 14 is stacked on the metal underlyinglayer 11 via the insulation layer 12. In other words, the insulationlayer 12 is interposed between the metal underlying layer 11 and theprotection layer 14.

The protection layer 14 includes a first protection layer 141 and asecond protection layer 142. The first protection layer 141 issuperposed on the insulation layer 12, and made of an insulativematerial such as SiN. The first protection layer 141 serves to preventSi, the predominant constituent of the semiconductor element 1, frombeing subjected to an excessive force, and is so-called a passivationlayer. The first protection layer 141 has a thickness of, for example, 1μm to 4 μm. The second protection layer 142 is superposed on the firstprotection layer 141, and made of an insulative material such aspolyimide. The second protection layer 142 has a thickness of, forexample, 3 μm to 6 μm.

Referring now to FIG. 4, the first protection layer 141 includes anupper face 141 a and a first side face 141 b. The upper face 141 a isoriented in the same direction as the first main surface 10 a of thesemiconductor element 1. The first side face 141 b is oriented to thebonding pad 13, in a direction orthogonal to the thickness direction(up-down direction in FIG. 4) of the semiconductor element 1.

The second protection layer 142 includes an upper face 142 a and asecond side face 142 b. The upper face 142 a is oriented in the samedirection as the first main surface 10 a of the semiconductor element 1.The second side face 142 b is oriented to the bonding pad 13, in adirection orthogonal to the thickness direction of the semiconductorelement 1. As shown in FIG. 4, in this embodiment the second side face142 b of the second protection layer 142 is recessed in a directionopposite to the bonding pad 13, with respect to the first side face 141b of the first protection layer 141.

The bonding pads 13 are formed on the first main surface 10 a. Thebonding pads 13 each include a first conductive layer 131, a secondconductive layer 132, and a third conductive layer 133. The first to thethird conductive layers 131 to 133 are each formed by metal plating.

The first conductive layer 131 covers the metal underlying layer 11. Thefirst conductive layer 131 is made of a metal having lower ionizationtendency than the metal underlying layer 11. The first conductive layer131 has higher hardness than the metal underlying layer 11. For example,the first conductive layer 131 made of Ni satisfies such properties. Thefirst conductive layer 131 has a thickness of, for example, 2 μm to 9μm. The periphery of the first conductive layer 131 is in close contactwith the surface of the protection layer 14. The first conductive layer131 is thicker than the first protection layer 141. In contrast, thefirst conductive layer 131 is thinner than the overall thickness of theprotection layer 14 (total of thicknesses of first protection layer 141and second protection layer 142). In this embodiment, accordingly, thefirst conductive layer 131 covers the entirety of the first side face141 b of the first protection layer 141 and a part of the second sideface 142 b of the second protection layer 142.

The second conductive layer 132 covers the first conductive layer 131.The second conductive layer 132 is made of a metal having lowerionization tendency than the first conductive layer 131. The secondconductive layer 132 has higher hardness than the first conductive layer131. For example, the second conductive layer 132 made of Pd satisfiessuch properties. The second conductive layer 132 has a thickness of, forexample, 0.1 μm to 0.5 μm. The periphery of the second conductive layer132 is in close contact with the surface of the protection layer 14. Thesecond conductive layer 132 is thinner than the second protection layer142. In this embodiment, the second conductive layer 132 covers a partof the second side face 142 b of the second protection layer 142.

The third conductive layer 133 covers the second conductive layer 132.The third conductive layer 133 is made of a metal having lowerionization tendency than the second conductive layer 132. For example,the third conductive layer 133 made of Au satisfies such properties. Thethird conductive layer 133 has a thickness of, for example, 10 nm to 0.1μm. The periphery of the third conductive layer 133 is in close contactwith the surface of the protection layer 14. The third conductive layer133 is thinner than the second protection layer 142. In this embodiment,the third conductive layer 133 covers a part of the second side face 142b of the second protection layer 142. In addition, in this embodimentthe overall thickness of the bonding pad 13 is thinner than the overallthickness of the protection layer 14. Accordingly, the bonding padleaves the upper face 142 a of the second protection layer 142 exposed.

As shown in FIG. 1, the wires 2 are each bonded to the first mainsurface 10 a of the semiconductor element 1. The wires 2 are also bondedto the sub electrode 32. The wire 2 may be made of, for example, Cu, Au,or Ag. In this embodiment, the wire 2 is made of Cu.

The wire 2 includes bonding sections 21 and 22, and a bridge section 23.

The bonding section 21 corresponds to the portion bonded to thesemiconductor element 1. To be more detailed, the bonding section 21 isbonded to the third conductive layer 133 (bonding pad 13) of thesemiconductor element 1, as shown in FIG. 3. In the manufacturingprocess of the semiconductor device A1, the bonding section 21 is bondedprior to the bonding section 22. Accordingly, the bonding section 21 isa first bonding section.

The bonding section 22 corresponds to the portion bonded to the subelectrode 32. In the manufacturing process of the semiconductor deviceA1, the bonding section 22 is bonded after the bonding section 21.Accordingly, the bonding section 22 is a second bonding section. Thebonding section 22 includes a joint region with the sub electrode 32,extending in one direction.

The bridge section 23 continuously extends to the bonding section 21 andthe bonding section 22. The bridge section 23 extends linearly, and hasa circular cross-section.

The sub electrode 32 is made of a conductive material. The sub electrode32 originates from a lead frame. Though not illustrated in detail, thesub electrode 32 includes a Cu portion and an Ag layer. The Cu portionincludes the Ag layer formed therein. The Cu portion is thicker than theAg layer. To the Ag layer, the wire 2 is bonded.

The main electrode 31 is made of a conductive material. The mainelectrode 31 originates from the lead frame. The main electrode 31 alsoincludes the Cu portion and the Ag layer like the sub electrode 32,however since the Cu portion and the Ag layer are configured in the sameway as above, the description will not be repeated. The semiconductorelement 1 is mounted on the main electrode 31 via an adhesive layer.

The sealing resin 5 encloses therein the semiconductor element 1 and thewires 2. More specifically, the sealing resin 5 covers the semiconductorelement 1, the wires 2, the main electrode 31, and the sub electrode 32.The sealing resin 5 is, for example, made of an epoxy resin. An end faceof the sub electrode 32 is exposed from the sealing resin 5. The exposedend face corresponds to the cut section formed when the lead frame iscut.

Referring now to FIG. 5 to FIG. 13, a manufacturing method of thesemiconductor device A1 will be described.

Referring first to FIG. 5, the metal underlying layer 11 is formed onthe semiconductor element 1. The metal underlying layer 11 iselectrically connected to a predetermined position of a non-illustratedfunctional circuit formed on the first main surface 10 a of thesemiconductor element 1. The metal underlying layer 11 may be formedinto a pattern, for example by Al plating. The metal underlying layer 11is formed in a thickness of, for example, 0.5 μm to 5 μm.

Referring to FIG. 6, the insulation layer 12 is formed. Although theformation method of the insulation layer 12 is not specifically limited,for example a deposition process such as chemical vapor deposition (CVD)may be employed to form a thin film of SiO₂ on a predetermined positionof the metal underlying layer 11.

Proceeding to FIG. 7, the first protection layer 141 and the secondprotection layer 142 are formed. To form the first protection layer 141and the second protection layer 142, for example, first a SiN layer anda polyimide layer are formed all over. The SiN layer is formed in athickness of, for example, 1 μm to 4 μm. The polyimide layer is formedin a thickness of, for example, 3 μm to 6 μm. Then the polyimide layerand the SiN layer are partially removed through a patterning processsuch as etching, so as to expose the metal underlying layer 11. Thesecond side face 142 b and the first side face 141 b can be thus formed.To partially remove the polyimide layer and the SiN layer, for examplean anisotropic dry etching process with a mask may be employed. Topartially remove the polyimide layer and the SiN layer, masks differentin opening pattern from each other are employed. The opening of the maskfor the polyimide layer (second protection layer 142) is larger than theopening of the mask for the SiN layer (first protection layer 141). Withsuch arrangements, the first protection layer 141 and the secondprotection layer 142 can be formed such that the second side face 142 bis recessed with respect to the first side face 141 b.

Proceeding to FIG. 8, the bonding pad 13 is formed. To form the bondingpad 13, the first conductive layer 131, the second conductive layer 132,and the third conductive layer 133 are stacked on the region where themetal underlying layer 11 is exposed. The first conductive layer 131 isformed in a thickness of, for example, 2 μm to 9 μm. The secondconductive layer 132 is formed in a thickness of, for example, 0.1 μm to0.5 μm, and the third conductive layer 133 is formed in a thickness of,for example, 10 nm to 0.1 μm. The first to the third conductive layers131 to 133 are each formed by metal plating, for example anon-electrolytic Ni/Pd/Au plating process. Through the mentionedprocess, the periphery of the bonding pad 13 (first conductive layer131, second conductive layer 132, and third conductive layer 133) entersinto close contact with the surface of the protection layer 14 (firstprotection layer 141 and second protection layer 142), so as to cover apart of the protection layer 14.

Proceeding to FIG. 9, a lead frame 3 is prepared. The lead frame 3includes portions to be formed into the main electrode 31 and the subelectrode 32. The lead frame 3 also includes the Cu portion and the Aglayer. The Cu portion and the Ag layer are the same as those describedabove with reference to the main electrode 31 and the sub electrode 32,and therefore the description will not be repeated.

Proceeding to FIG. 10, the semiconductor element 1 is mounted on thelead frame 3 (main electrode 31). For example, a bonding material suchas a silver paste or solder may be employed to mount the semiconductorelement 1 on the main electrode 31.

Proceeding to FIG. 11, the wires 2 are bonded to the semiconductorelement 1 and the sub electrode 32. For the bonding of the wires 2, forexample a non-illustrated capillary is employed. More specifically,first the wire 2 is bonded to the semiconductor element 1 (firstbonding). To do so, the wire 2 is passed through the capillary and drawnout from the tip portion of the capillary, and the leading end portionof the wire 2 is molten. Then ultrasonic vibration is applied to theleading end portion of the wire 2 while the leading end portion of thewire 2 is pressed against the bonding pad 13 of the semiconductorelement 1, by the capillary. Through such a process, the leading endportion of the wire 2 is bonded to the semiconductor element 1 (bondingpad 13). Then the capillary is separated from the semiconductor element1. At this point, the bonding section 21 shown in FIG. 3 is formed.

Then the capillary is moved while drawing out the wire 2 so as to form awire loop, and the wire 2 is bonded to the sub electrode 32 (secondbonding). The ultrasonic vibration is applied to the wire 2 while thewire 2 is pressed against the sub electrode 32, so as to fix the wire 2to the sub electrode 32 (Ag layer in this embodiment). When the wire 2is fixed to the sub electrode 32, the capillary is lifted with the wire2 passed therethrough being clamped, to thereby cut the wire 2 (notshown). At this point, the semiconductor element 1 and the sub electrode32 are electrically connected to each other via the wire loop made ofthe wire 2 (see FIG. 11). Then a plurality of wires 2 are bonded in thesame manner.

Then the sealing resin 5 covering the wire 2 and the lead frame 3 isformed as shown in FIG. 12, with a desired mold.

Referring to FIG. 13, the sealing resin 5 and the lead frame 3 are cutinto individual pieces, after the formation of the sealing resin 5.Thus, a plurality of semiconductor devices A1 can be obtained.

The semiconductor device A1 provides the following advantageous effects.

In this embodiment, the bonding pad 13 is made of a metal having lowerionization tendency than the metal underlying layer 11, and theionization tendency of the first conductive layer 131, the secondconductive layer 132, and the third conductive layer 133 becomes lowerin the order in which these layers are stacked on the metal underlyinglayer 11. Such a configuration effectively prevents the corrosion of themetal underlying layer 11 and the first conductive layer 131 located onthe lower side.

The periphery of the bonding pad 13 (first conductive layer 131, secondconductive layer 132, and third conductive layer 133) is in closecontact with the surface of the protection layer 14 (first protectionlayer 141 and second protection layer 142), so as to cover a part of theprotection layer 14. The mentioned configuration effectively preventsthe protection layer 14 from being delaminated, because of the closecontact between the bonding pad 13 and the protection layer 14, comparedwith the case where, unlike in this embodiment, the protection layer isformed so as to cover the periphery of the bonding pad. Accordingly, thedurability of the semiconductor device A1 can be improved.

In addition, since the periphery of the bonding pad 13 covers a part ofthe surface of the protection layer 14, the region where the first tothe third conductive layers 131 to 133 constituting the bonding pad 13are formed corresponds to the region where the metal of the bonding pad13 is exposed, in a view in the thickness direction of the semiconductorelement 1. Accordingly, the formation region of the first to the thirdconductive layers 131 to 133 constituting the bonding pad 13 can be madesmaller, compared with the case where, unlike in this embodiment, theprotection layer is formed so as to cover the periphery of the bondingpad. Such a configuration contributes to reducing the size of thesemiconductor device A1.

In this embodiment, the second side face 142 b of the second protectionlayer 142 is recessed in the direction opposite to the bonding pad 13,with respect to the first side face 141 b of the first protection layer141. In addition, the first conductive layer 131 is thicker than thefirst protection layer 141, and is in close contact with the entirety ofthe first side face 141 b of the first protection layer 141, a part ofthe upper face 141 a, and a part of the second side face 142 b of thesecond protection layer 142, so as to collectively cover the mentionedregions. Therefore, the first conductive layer 131 (bonding pad 13)effectively prevents the delamination of the first protection layer 141.The mentioned configuration further prevents moisture or a foreignmatter from intruding as far as the metal underlying layer 11 throughthe interface between the first conductive layer 131 (bonding pad 13)and the protection layer 14.

The first conductive layer 131 and the second conductive layer 132 havehigher hardness than the metal underlying layer 11. Accordingly, eventhough the pressure of the capillary is applied to the bonding pad 13during the bonding process of the wire 2 to the bonding pad 13, thebonding pad 13 and the metal underlying layer 11 can be prevented frombeing cracked or damaged.

FIG. 14 to FIG. 17 illustrate variations of the semiconductor device A1.

A semiconductor device A1′ shown in FIG. 14 and FIG. 15 is differentfrom the semiconductor device A1 in the thickness of the bonding pad 13.

More specifically, in this variation the first conductive layer 131 inthe semiconductor device A1′ is thinner than e first conductive layer131 in the semiconductor device A1. The first conductive layer 131 isthinner than the first protection layer 141. In addition, the overallthickness of the bonding pad 13 (total of thicknesses of firstconductive layer 131, second conductive layer 132, and third conductivelayer 133) is thinner than the first protection layer 141. Accordingly,the bonding pad 13 covers a part of the first side face 141 b of thefirst protection layer 141, and exposes the second protection layer 142.The semiconductor device A1′ thus configured also provides the sameadvantageous effects as those provided by the semiconductor device A1.

A semiconductor device A1″ shown in FIG. 16 and FIG. 17 is differentfrom the semiconductor device A1 in the shape of the first side face 141b of the first protection layer 141, and the shape of the second sideface 142 b of the second protection layer 142.

More specifically, in the semiconductor device A1″ according to thisvariation, the first side face 141 b of the first protection layer 141and the second side face 142 b of the second protection layer 142 areeach inclined so as to be more distant from the bonding pad 13, in thedirection away from the semiconductor element 1 in the thicknessdirection of the semiconductor element 1. The first side face 141 b andthe second side face 142 b inclined as above may be formed, for example,by removing a part of the polyimide layer and the SiN layer respectivelyconstituting the second protection layer 142 and the first protectionlayer 14, through an isotropic wet etching process.

The first conductive layer 131 is thicker than the first protectionlayer 141, but thinner than the overall thickness of the protectionlayer 14 (total of thicknesses of first protection layer 141 and secondprotection layer 142). Therefore, the first conductive layer 131 coversthe entirety of the first side face 141 b of the first protection layer141 and a part of the second side face 142 b of the second protectionlayer 142. The second conductive layer 132 is thinner than the secondprotection layer 142. The second conductive layer 132 covers a part ofthe second side face 142 b of the second protection layer 142. The thirdconductive layer 133 is thinner than the second protection layer 142.The third conductive layer 133 covers a part of the second side face 142b of the second protection layer 142. The overall thickness of thebonding pad 13 is thinner than the overall thickness of the protectionlayer 14. Because of the mentioned configuration, the bonding pad 13leaves the upper face 142 a of the second protection layer 142 exposed.

The semiconductor device A1″ thus configured also provides the sameadvantageous effects as those provided by the semiconductor device A1.Further, forming the first side face 141 b and the second side face 142b in the inclined shape as above enables the bonding pad 13 (first tothird conductive layers 131, 132, 133) covering the first side face 141b and the second side face 142 b to more effectively prevent the firstprotection layer 141 and the second protection layer 142 from beingdelaminated from the end portions thereof (vicinity of first side face141 b and second side face 142 b), thereby further assuring theprevention of the delamination of the protection layer 14.

FIG. 18 and FIG. 19 illustrate a semiconductor device according to asecond embodiment of the present invention. In FIG. 18 and thesubsequent drawings, the elements same as or similar to those of theforegoing embodiment are given the same numeral, and the descriptionthereof may be omitted where appropriate. In FIG. 19, the wires 2 andthe sealing resin 5 are omitted.

The semiconductor device A2 according to this embodiment is differentfrom the foregoing embodiment in the configuration of the bonding pad 13and the protection layer 14.

The protection layer 14 includes the first protection layer 141 and thesecond protection layer 142. The first protection layer 141 is made ofan insulative material such as SiN. The first protection layer 141 has athickness of, for example, 2 μm to 4 μm. The second protection layer 142is superposed on the first protection layer 141, and made of aninsulative material such as polyimide. The second protection layer 142has a thickness of, for example, 3 μm to 6 μm.

Referring to FIG. 19, the first protection layer 141 includes the upperface 141 a and the first side face 141 b. In this embodiment, the firstside face 141 b is inclined so as to be more distant from the bondingpad 13, in the direction away from the semiconductor element 1 in thethickness direction of the semiconductor element 1.

The second protection layer 142 includes a main layer 143 and an eavesportion 144. The main layer 143 corresponds to the portion superposed onthe first protection layer 141. The eaves portion 144 protrudes from themain layer 143 toward the bonding pad 13, in the direction orthogonal tothe thickness direction of the semiconductor element 1. In FIG. 19, theboundary between the main layer 143 and the eaves portion 144 isindicated by broken lines, for the sake of clarity. The eaves portion144 includes a side face 144 b and a lower face 144 c. The side face 144b is oriented to the bonding pad 13 in the direction orthogonal to thethickness direction of the semiconductor element 1. The lower face 144 cis oriented to the semiconductor element 1, in the thickness directionof the semiconductor element 1. In this embodiment, the side face 144 bis inclined so as to be more distant from the bonding pad 13, in thedirection away from the semiconductor element 1 in the thicknessdirection of the semiconductor element 1.

The bonding pad 13 includes the first conductive layer 131, the secondconductive layer 132, and the third conductive layer 133. The first tothe third conductive layers 131 to 133 are each formed by metal plating.

The first conductive layer 131 covers the metal underlying layer 11. Thefirst conductive layer 131 is made of a metal having lower ionizationtendency than the metal underlying layer 11. The first conductive layer131 has higher hardness than the metal underlying layer 11. For example,the first conductive layer 131 made of Ni satisfies such properties. Thefirst conductive layer 131 has a thickness of, for example, 1 μm to 3μm. The periphery of the first conductive layer 131 is in close contactwith the surface of the protection layer 14. The first conductive layer131 is thinner than the first protection layer 141. In this embodiment,the first conductive layer 131 covers a part of the first side face 141b of the first protection layer 141.

The second conductive layer 132 covers the first conductive layer 131.The second conductive layer 132 is made of a metal having lowerionization tendency than the first conductive layer 131. The secondconductive layer 132 has higher hardness than the metal underlying layer11. For example, the second conductive layer 132 made of Pd satisfiessuch properties. The second conductive layer 132 has a thickness of, forexample, 0.1 μm to 0.5 μm. The periphery of the second conductive layer132 is in close contact with the surface of the protection layer 14. Thesecond conductive layer 132 is thinner than the first protection layer141. In this embodiment, the second conductive layer 132 covers a partof the first side face 141 b of the first protection layer 141.

The third conductive layer 133 covers the second conductive layer 132.The third conductive layer 133 is made of a metal having lowerionization tendency than the second conductive layer 132. For example,the third conductive layer 133 made of Au satisfies such properties. Thethird conductive layer 133 has a thickness of, for example, 10 nm to 0.1μm. The periphery of the third conductive layer 133 is in close contactwith the surface of the protection layer 14. The third conductive layer133 is thinner than the first protection layer 141. In this embodiment,the third conductive layer 133 covers a part of the first side face 141b of the first protection layer 141. In addition, in this embodiment theoverall thickness of the bonding pad 13 is thinner than the overallthickness of the first protection layer 141. Accordingly, the lower face144 c of the eaves portion 144 is more distant from the semiconductorelement 1 than is the upper face of the bonding pad 13 (upper face ofthird conductive layer 133). Thus, the bonding pad 13 leaves the eavesportion 144 (second protection layer 142) exposed.

Referring now to FIG. 20 to FIG. 23, a manufacturing method of thesemiconductor device A2 will be described. Here, FIG. 20 to FIG. 23represent the formation process of the protection layer 14 and thebonding pad 13 (corresponding to manufacturing method of semiconductordevice A1 shown in FIG. 7 and FIG. 8). The remaining process formanufacturing the semiconductor device A2 is the same as that of thesemiconductor device A1, and therefore the corresponding descriptionwill not be repeated.

Referring to FIG. 20, the first protection layer 141 and the secondprotection layer 142 are formed. To form the first protection layer 141and the second protection layer 142, for example, first a SiN layer anda polyimide layer are formed all over. The SiN layer is formed in athickness of, for example, 2 μm to 4 μm. The polyimide layer is formedin a thickness of, for example, 3 μm to 6 μm.

Referring then to FIG. 21, the polyimide layer is partially removedthrough a patterning process such as etching, so as to expose a part ofthe upper face of the SiN layer thus to form the side face 144 b. Topartially remove the polyimide layer, for example an isotropic wetetching process with a mask may be employed. Through the mentionedprocess, the second protection layer 142 having the inclined side face144 b can be formed. At this point, the entirety of the secondprotection layer 142 is superposed on the SiN layer, and hence there isno distinction between the main layer 143 and the eaves portion 144.

Proceeding to FIG. 22, the SiN layer is partially removed through apatterning process such as etching, so as to expose the metal underlyinglayer 11. To partially remove the SiN layer, for example an isotropicwet etching process with a mask may be employed. To partially remove thepolyimide layer and the SiN layer, a mask of the same opening pattern asthe mask for partially removing the polyimide layer is employed. Throughthe mentioned process, the first protection layer 141 having theinclined first side face 141 b can be formed. In addition, with thepartial removal of the SiN layer, the eaves portion 144 becomesdistinguishable from the main layer 143, in the second protection layer142.

Proceeding to FIG. 23, the bonding pad 13 is formed. To form the bondingpad 13, the first conductive layer 131, the second conductive layer 132,and the third conductive layer 133 are stacked on the region where themetal underlying layer 11 is exposed. The first conductive layer 131 isformed in a thickness of, for example, 1 μm to 3 μm. The secondconductive layer 132 is formed in a thickness of, for example, 0.1 μm to0.5 μm, and the third conductive layer 133 is formed in a thickness of,for example, 10 nm to 0.1 μm. The first to the third conductive layers131 to 133 are each formed by metal plating, for example anon-electrolytic Ni/Pd/Au plating process. Through the mentionedprocess, the periphery of the bonding pad 13 (first conductive layer131, second conductive layer 132, and third conductive layer 133) entersinto close contact with the surface of the protection layer 14 (firstprotection layer 141), so as to cover a part of the protection layer 14.

The semiconductor device A2 provides the following advantageous effects.

In this embodiment, the bonding pad 13 is made of a metal having lowerionization tendency than the metal underlying layer 11, and theionization tendency of the first conductive layer 131, the secondconductive layer 132, and the third conductive layer 133 becomes lowerin the order in which these layers are stacked on the metal underlyinglayer 11. Such a configuration effectively prevents the corrosion of themetal underlying layer 11 and the first conductive layer 131 located onthe lower side.

The periphery of the bonding pad 13 (first conductive layer 131, secondconductive layer 132, and third conductive layer 133) is in closecontact with the surface of the protection layer 14 (first protectionlayer 141), so as to cover a part of the protection layer 14. Thementioned configuration effectively prevents the protection layer 14from being delaminated, because of the close contact between the bondingpad 13 and the protection layer 14, compared with the case where, unlikein this embodiment, the protection layer is formed so as to cover theperiphery of the bonding pad. Accordingly, the durability of thesemiconductor device A2 can be improved.

In addition, since the periphery of the bonding pad 13 covers a part ofthe surface of the protection layer 14, the region where the first tothe third conductive layers 131 to 133 constituting the bonding pad 13are formed generally corresponds to the region where the metal of thebonding pad 13 is exposed, in a view in the thickness direction of thesemiconductor element 1. Accordingly, the formation region of the firstto the third conductive layers 131 to 133 constituting the bonding pad13 can be made smaller, compared with the case where, unlike in thisembodiment, the protection layer is formed so as to cover the peripheryof the bonding pad. Such a configuration contributes to reducing thesize of the semiconductor device A2.

In this embodiment, the first conductive layer 131 is in close contactwith the insulation layer 12 and a part of the first side face 141 b ofthe first protection layer 141, so as to collectively cover thementioned regions. The first side face 141 b is inclined as describedabove. Therefore, the first conductive layer 131 (bonding pad 13)effectively prevents the delamination of the first protection layer 141.The mentioned configuration further prevents moisture or a foreignmatter from intruding as far as the metal underlying layer 11 throughthe interface between the first conductive layer 131 (bonding pad 13)and the protection layer 14 (first protection layer 141).

The first conductive layer 131 and the second conductive layer 132 havehigher hardness than the metal underlying layer 11. Accordingly, eventhough the pressure of the capillary is applied to the bonding pad 13during the bonding process of the wire 2 to the bonding pad 13, thebonding pad 13 and the metal underlying layer 11 can be prevented frombeing cracked or damaged.

FIG. 24 and FIG. 25 illustrate a semiconductor device according to athird embodiment of the present invention. In FIG. 25, the wires 2 andthe sealing resin 5 are omitted.

The semiconductor device A3 according to this embodiment is differentfrom the first embodiment in the configuration of the bonding pad 13 andthe protection layer 14. The configuration of the protection layer 14 isthe same as that of the second embodiment. Hereunder, the bonding pad 13will be primarily focused on, and the description of the protectionlayer 14 may be omitted where appropriate.

The protection layer 14 includes a first protection layer 141 and asecond protection layer 142. The first protection layer 141 is made ofan insulative material such as SiN. The first protection layer 141 has athickness of, for example, 2 μm to 4 μm. The second protection layer 142is superposed on the first protection layer 141, and made of aninsulative material such as polyimide. The second protection layer 142has a thickness of, for example, 3 μm to 6 μm.

The bonding pad 13 includes the first conductive layer 131, the secondconductive layer 132, and the third conductive layer 133. The first tothe third conductive layers 131 to 133 are each formed by metal plating.

The first conductive layer 131 covers the metal underlying layer 11. Thefirst conductive layer 131 is made of a metal having lower ionizationtendency than the metal underlying layer 11. The first conductive layer131 has higher hardness than the metal underlying layer 11. For example,the first conductive layer 131 made of Ni satisfies such properties. Thefirst conductive layer 131 has a thickness of, for example, 6 μm to 12μm. The periphery of the first conductive layer 131 is in close contactwith the surface of the protection layer 14. The first conductive layer131 is thicker than the overall thickness of the protection layer 14(total of thicknesses of first protection layer 141 and secondprotection layer 142). In this embodiment, the first conductive layer131 covers a part of the first side face 141 b of the first protectionlayer 141 and the entirety of the side face 144 b. However, the firstconductive layer 131 leaves the lower face 144 c exposed. Accordingly, avoid 15 is defined by the lower face 144 c, the first side face 141 b ofthe first protection layer 141, and the first conductive layer 131.

The second conductive layer 132 covers the first conductive layer 131.The second conductive layer 132 is made of a metal having lowerionization tendency than the first conductive layer 131. The secondconductive layer 132 has higher hardness than the metal underlying layer11. For example, the second conductive layer 132 made of Pd satisfiessuch properties. The second conductive layer 132 has a thickness of, forexample, 0.1 μm to 0.5 μm. The periphery of the second conductive layer132 is in close contact with the surface of the protection layer 14. Inthis embodiment, the second conductive layer 132 covers a part of theupper face 142 a of the second protection layer 142 extending as far asthe side face 144 b.

The third conductive layer 133 covers the second conductive layer 132.The third conductive layer 133 is made of a metal having lowerionization tendency than the second conductive layer 132. For example,the third conductive layer 133 made of Au satisfies such properties. Thethird conductive layer 133 has a thickness of, for example, 10 nm to 0.1μm. The periphery of the third conductive layer 133 is in close contactwith the surface of the protection layer 14. In this embodiment, thethird conductive layer 133 covers a part of the upper face 142 a of thesecond protection layer 142.

Referring now to FIG. 26 to FIG. 29, a manufacturing method of thesemiconductor device A3 will be described. Here, FIG. 26 to FIG. 29represent the formation process of the bonding pad 13 (corresponding tomanufacturing method of semiconductor device A2 shown in FIG. 23). Theremaining process for manufacturing the semiconductor device A3 is thesame as that of the semiconductor device A2, and therefore thecorresponding description will not be repeated.

To form the bonding pad 13, the first conductive layer 131, the secondconductive layer 132, and the third conductive layer 133 are stacked onthe region where the metal underlying layer 11 is exposed. The firstconductive layer 131 is formed in a thickness of, for example, 6 μm to12 μm. The second conductive layer 132 is formed in a thickness of, forexample, 0.1 μm to 0.5 μm, and the third conductive layer 133 is formedin a thickness of, for example, 10 nm to 0.1 μm. The first to the thirdconductive layers 131 to 133 are each formed by metal plating, forexample a non-electrolytic Ni/Pd/Au plating process.

FIG. 26 to FIG. 28 illustrate the formation process of the firstconductive layer 131. Through the plating process, the first conductivelayer 131 grows so as to increase the thickness. FIG. 26 illustrates astage where the first conductive layer 131 is still relatively thin, andthe upper face of the first conductive layer 131 (oriented in the samedirection as the first main surface 10 a of the semiconductor element 1)is closer to the semiconductor element 1 than is the upper face 141 a ofthe first protection layer 141, in the thickness direction of thesemiconductor element 1. At this point, the periphery of the firstconductive layer 131 proceeds toward the first protection layer 141 inthe direction orthogonal to the thickness direction of the semiconductorelement 1, so as to cover a part of the first side face 141 b of thefirst protection layer 141. FIG. 27 illustrates a stage subsequent toFIG. 26, where the first conductive layer 131 has slightly growncompared with FIG. 26. At this point, the upper face of the firstconductive layer 131 is more distant from the semiconductor element 1than is the upper face 141 a of the first protection layer 141, but iscloser to the semiconductor element 1 than is the upper face 142 a ofthe second protection layer 142, in the thickness direction of thesemiconductor element 1. Here, the first conductive layer 131 abutsagainst a leading edge 144 d (see FIG. 28) formed at the intersection ofthe side face 144 b and the lower face 144 c, to thereby stop proceedingfurther toward the first protection layer 141. Thus, the void 15 isdefined by the lower face 144 c of the eaves portion 144, the first sideface 141 b of the first protection layer 141, and the first conductivelayer 131.

FIG. 28 illustrates a stage where the formation of the first conductivelayer 13 has been completed. At this point, the upper face of the firstconductive layer 131 more distant from the semiconductor element 1 thanis the upper face 142 a of the second protection layer 142 in thethickness direction of the semiconductor element 1, and the firstconductive layer 131 covers a part of the upper face 142 a of the secondprotection layer 142.

Proceeding to FIG. 29, the second conductive layer 132 and the thirdconductive layer 133 are sequentially superposed on the first conductivelayer 131. The bonding pad 13 can thus be obtained.

The semiconductor device A3 provides the following advantageous effects.

In this embodiment, the bonding pad 13 is made of a metal having lowerionization tendency than the metal underlying layer 11, and theionization tendency of the first conductive layer 131, the secondconductive layer 132, and the third conductive layer 133 becomes lowerin the order in which these layers are stacked on the metal underlyinglayer 11. Such a configuration effectively prevents the corrosion of themetal underlying layer 11 and the first conductive layer 131 located onthe lower side.

The periphery of the bonding pad 13 (first conductive layer 131, secondconductive layer 132, and third conductive layer 133) is in closecontact with the surface of the protection layer 14 (first protectionlayer 141 and first protection layer 141), so as to cover a part of theprotection layer 14. The mentioned configuration effectively preventsthe protection layer 14 from being delaminated, because of the closecontact between the bonding pad 13 and the protection layer 14, comparedwith the case where, unlike in this embodiment, the protection layer isformed so as to cover the periphery of the bonding pad. Accordingly, thedurability of the semiconductor device A3 can be improved.

In addition, since the periphery of the bonding pad 13 covers a part ofthe surface of the protection layer 14, the region where the first tothe third conductive layers 131 to 133 constituting the bonding pad 13are formed corresponds to the region where the metal of the bonding pad13 is exposed, in a view in the thickness direction of the semiconductorelement 1. Accordingly, the formation region of the first to the thirdconductive layers 131 to 133 constituting the bonding pad 13 can be madesmaller, compared with the case where, unlike in this embodiment, theprotection layer is formed so as to cover the periphery of the bondingpad. Such a configuration contributes to reducing the size of thesemiconductor device A3.

In this embodiment, the first conductive layer 131 is in close contactwith the insulation layer 12, a part of the first side face 141 b of thefirst protection layer 141, the entirety of the side face 144 b of thesecond protection layer 142, and a part of the upper face 142 a of thesecond protection layer 142, so as to cover the mentioned regions.Therefore, the first conductive layer 131 (bonding pad 13) effectivelyprevents the delamination of the protection layer 14 (first protectionlayer 141 and first protection layer 141). The mentioned configurationfurther prevents moisture or a foreign matter from intruding as far asthe metal underlying layer 11 through the interface between the firstconductive layer 131 (bonding pad 13) and the protection layer 14.

Further, the configuration in which the first side face 141 b and theside face 144 b are inclined as above, the bonding pad 13 (firstconductive layer 131) covering these portions effectively prevents thefirst protection layer 141 and the second protection layer 142 frombeing separated from the end portion (vicinity of first side face 141 band side face 144 b), thereby further assuring the prevention of thedelamination of the protection layer 14.

The first conductive layer 131 and the second conductive layer 132 havehigher hardness than the metal underlying layer 11. Accordingly, eventhough the pressure of the capillary is applied to the bonding pad 13during the bonding process of the wire 2 to the bonding pad 13, thebonding pad 13 and the metal underlying layer 11 can be prevented frombeing cracked or damaged.

FIG. 30 and FIG. 31 illustrate a variation of the semiconductor deviceA3. The semiconductor device A3′ shown in FIG. 30 and FIG. 31 isdifferent from the semiconductor device A3 in the thickness of thebonding pad 13.

More specifically, in the semiconductor device A3′ according to thisvariation, the first conductive layer 131 is thinner than that of thesemiconductor device A3. The first conductive layer 131 is thicker thanthe first protection layer 141, but thinner than the overall thicknessof the protection layer 14 (total of thicknesses of first protectionlayer 141 and second protection layer 142). In addition, the overallthickness of the bonding pad 13 (total of thicknesses of firstconductive layer 131, second conductive layer 132, and third conductivelayer 133) is also thinner than the overall thickness of the protectionlayer 14. Accordingly, the bonding pad 13 (first to third conductivelayers 131 to 133) covers a part of the side face 144 b, and leaves theupper face 142 a of the second protection layer 142 exposed. Thesemiconductor device A3′ thus configured also provides the sameadvantageous effects as those provided by the semiconductor device A3.

Semiconductor devices of the invention are not limited to the aboveembodiments. Specific configurations of the device of the invention maybe modified in various manners.

The invention claimed is:
 1. A semiconductor device comprising: asemiconductor element including a first main surface and a second mainsurface that are spaced apart from each other in a thickness direction;and a wire, wherein the semiconductor element includes: a metalunderlying layer formed on the first main surface; a bonding pad formedon the metal underlying layer and to which the wire is bonded; and aninsulative protection layer formed on the first main surface andsurrounding the bonding pad as viewed in the thickness direction, thebonding pad includes: a first conductive layer covering the metalunderlying layer and made of a metal having a lower ionization tendencythan the metal underlying layer; and a second conductive layer coveringthe first conductive layer and made of a metal having a lower ionizationtendency than the first conductive layer, the first conductive layer andthe second conductive layer have peripheries, respectively, that are inclose contact with the protection layer and cover a part of theprotection layer, a part of the metal underlying layer is sandwichedbetween the first main surface and the protection layer so that saidpart of the metal underlying layer does not directly contact the firstconductive layer, the protection layer does not directly contact anypart of an entirety of a top surface of the bonding pad, the protectionlayer includes a first protection layer and a second protection layerformed on the first protection layer, the first protection layer and thesecond protection layer include a first side face and a second sideface, respectively, that are oriented to the bonding pad in a directionorthogonal to the thickness direction, the second side face of thesecond protection layer is shifted in a direction opposite to thebonding pad with respect to the first side face of the first protectionlayer, and the first conductive layer is held in direct contact with anentirety of the first side face of the first protection layer, a part ofan upper face of the first protection layer, and a part of the secondside face of the second protection layer.
 2. The semiconductor deviceaccording to claim 1, further comprising an insulation layer interposedbetween the protection layer and the metal underlying layer.
 3. Thesemiconductor device according to claim 1, wherein the second conductivelayer covers a part of the second side face of the second protectionlayer and exposes an upper face of the second protection layer.
 4. Thesemiconductor device according to claim 1, wherein the first side faceof the first protection layer and the second side face of the secondprotection layer are each inclined so as to be more distant from thebonding pad with increasing distance from the semiconductor element inthe thickness direction.
 5. The semiconductor device according to claim1, wherein the first protection layer is made of SiN.
 6. Thesemiconductor device according to claim 1, wherein the first conductivelayer contains Ni.
 7. The semiconductor device according to claim 1,wherein the second conductive layer contains Pd.
 8. The semiconductordevice according to claim 1, wherein the first conductive layer and thesecond conductive layer have a higher hardness than the metal underlyinglayer.
 9. The semiconductor device according to claim 1, wherein thefirst conductive layer is thicker than the second conductive layer. 10.The semiconductor device according to claim 1, wherein the firstconductive layer and the second conductive layer are formed by metalplating.
 11. The semiconductor device according to claim 1, wherein thebonding pad includes a third conductive layer that covers and is thinnerthan the second conductive layer, and the third conductive layer is madeof a metal having a lower ionization tendency than the second conductivelayer.
 12. The semiconductor device according to claim 1, wherein thewire is made of a Cu-based metal.